Abstract
PurposeTo evaluate whether quantitative [18F]FDG-PET/CT assessment, including radiomic analysis of [18F]FDG-positive thyroid nodules, improved the preoperative differentiation of indeterminate thyroid nodules of non-Hürthle cell and Hürthle cell cytology.MethodsProspectively included patients with a Bethesda III or IV thyroid nodule underwent [18F]FDG-PET/CT imaging. Receiver operating characteristic (ROC) curve analysis was performed for standardised uptake values (SUV) and SUV-ratios, including assessment of SUV cut-offs at which a malignant/borderline neoplasm was reliably ruled out (≥ 95% sensitivity). [18F]FDG-positive scans were included in radiomic analysis. After segmentation at 50% of SUVpeak, 107 radiomic features were extracted from [18F]FDG-PET and low-dose CT images. Elastic net regression classifiers were trained in a 20-times repeated random split. Dimensionality reduction was incorporated into the splits. Predictive performance of radiomics was presented as mean area under the ROC curve (AUC) across the test sets.ResultsOf 123 included patients, 84 (68%) index nodules were visually [18F]FDG-positive. The malignant/borderline rate was 27% (33/123). SUV-metrices showed AUCs ranging from 0.705 (95% CI, 0.601–0.810) to 0.729 (0.633–0.824), 0.708 (0.580–0.835) to 0.757 (0.650–0.864), and 0.533 (0.320–0.747) to 0.700 (0.502–0.898) in all (n = 123), non-Hürthle (n = 94), and Hürthle cell (n = 29) nodules, respectively. At SUVmax, SUVpeak, SUVmax-ratio, and SUVpeak-ratio cut-offs of 2.1 g/mL, 1.6 g/mL, 1.2, and 0.9, respectively, sensitivity of [18F]FDG-PET/CT was 95.8% (95% CI, 78.9–99.9%) in non-Hürthle cell nodules. In Hürthle cell nodules, cut-offs of 5.2 g/mL, 4.7 g/mL, 3.4, and 2.8, respectively, resulted in 100% sensitivity (95% CI, 66.4–100%). Radiomic analysis of 84 (68%) [18F]FDG-positive nodules showed a mean test set AUC of 0.445 (95% CI, 0.290–0.600) for the PET model.ConclusionQuantitative [18F]FDG-PET/CT assessment ruled out malignancy in indeterminate thyroid nodules. Distinctive, higher SUV cut-offs should be applied in Hürthle cell nodules to optimize rule-out ability. Radiomic analysis did not contribute to the additional differentiation of [18F]FDG-positive nodules.Trial registration numberThis trial is registered with ClinicalTrials.gov: NCT02208544 (5 August 2014), https://clinicaltrials.gov/ct2/show/NCT02208544.
Highlights
An accurate diagnostic workup of cytologically indeterminate thyroid nodules is crucial to prevent futile diagnostic surgeries for benign nodules as well as to ensure timely diagnosis of malignant or borderline tumours
The EfFECTS trial was conducted in eight academic and seven community hospitals in the Netherlands with a high level of experience in the diagnosis and treatment of thyroid nodules and differentiated thyroid carcinoma (Supplementary data). [18F]FDG-PET/CT was performed in 132 patients with a solitary nodule or dominant nodule in multinodular disease from which indeterminate cytology was obtained, defined as at least two Bethesda III or one Bethesda IV cytology result
In the current side study of this randomised controlled trial, we showed that quantitative [18F]FDG-PET/CT analysis accurately ruled out malignancy in both non-Hürthle and Hürthle cell nodules, provided that different standardised uptake values (SUV) cut-offs were chosen for these two groups
Summary
An accurate diagnostic workup of cytologically indeterminate thyroid nodules is crucial to prevent futile diagnostic surgeries for benign nodules as well as to ensure timely diagnosis of malignant or borderline tumours. FLUS) and cytology suspicious for a follicular neoplasm (Bethesda IV, FN/SFN) or Hürthle cell neoplasm (Bethesda IV, HCN/SHCN), indeterminate thyroid nodules have an approximate 25% risk of malignancy [1,2,3]. With a limited 40% specificity, visual [18F]FDG-PET/CT assessment increased the post-test risk of malignancy but appeared unable to fully risk-stratify the approximately two-thirds visually [18F]FDG-positive nodules [4]. These results validated the findings from previously published, smaller, non-randomised studies [5,6,7,8,9,10,11,12]
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